1. Field of the Invention
This invention relates to laminates of microcomposite layers, particularly those of ordered polymer/sol-gel glass microcomposite layers laminated with glass adhesives and methods therefor.
2. The Prior Art
Ordered polymers are characterized by strong, stiff, rod-like molecules which exhibit high tensile strength but are of low compressive strength and poor interlaminar adhesion caused by buckling of the fibrillar network (of the rod-like molecule) during compression. Attempts have been made to increase such compressive strength by inserting a binder into such network which is compression resistant so as to obtain (microcomposite) structures of improved tensile strength and compressive strength.
Thus a process for fabricating such a composite in the form of a network of microfibrils of, eg. PBZT and PBO (defined below) and an interpenetrating binder of e.g. a sodium silicate mixture with a metal oxide therein is disclosed in U.S. Pat. No. 4,842,924 to R. J. Farris et al. (1989).
Another reference discloses biaxially-oriented film from ordered polymers of e.g. PBZT or PBO containing a binder of borosilicate glass in the microcomposite; see U.S. Pat. No. 4,845,150 to R. Kovak (Kovar) et al. (1989), which patents are herein incorporated by reference.
The above Kovak reference discloses preparing laminates of such microcomposite films by alternating PEEK resin film and PBZT film (with or without polyimide impregnation) in layers and applying heat and pressure thereto. A laminate of PEEK film and (impregnated) PBZT film, modified to improve compressive strength and interlaminar (between plies) strength is not suggested.
The above Farris reference states that films impregnated with matrix-forming material may be positioned in layers, e.g. per his FIG. 3, and subsequently solidified, so that the matrix material also serves to bond the individual microfibrillar network composite films together. This is a concurrent microcomposite-forming laminating step that requires e.g. 15-20% by weight of matrix material for good lamination of film layers at, however, the expense of tensile strength of such composite, particularly where such matrix material gels into a glass matrix. This is because the glass particles act as miniature knives which can cut the microfibrils when the so-impregnated film is under tension, to the detriment of the tensile strength thereof.
Clearly there is a need and market for a method for laminating microcomposite films of ordered polymers of good physical properties that overcome the above prior art shortcomings.
Reliable methods of laminating, e.g. PBZT/sol-gel glass microcomposite film layers are essential for production of high-performance applications, e.g. for spacecraft and tough, impact-resistant structures. This can place severe demands on PBZT/sol-gel microcomposite films and adhesive systems to provide adequate adhesion and interlaminar strength. The excellent chemical resistance of PBZT also makes it difficult to form strong bonds at the surface thereof, resulting in the need for surface treatment thereof or a means to impregnate such film with adhesive. In addition, the high strength and modulus of PBZT film, along with its outstanding thermal resistance means that high-performance, high-temperature adhesives must be selected to match the capabilities of such film. Accordingly, it is necessary to determine the proper surface treatment for PBZT/sol-gel film microcomposites and also to determine the suitable adhesives for laminating layers of such film together.
There has now been discovered a method for laminating microcomposite films of ordered polymers of various matrices wherein the plies thereof have a reduced amount of matrix or infiltrant therein and a reduced concentration of adhesive between such plies for the benefit of the tensile strength thereof, in which the infiltrant and adhesive can be of the same or different materials. Also discovered are the laminates produced by such method.